itsmoked
Electrical
- Feb 18, 2005
- 19,114
We have a small plant that processes about 20g/min. We're failing to get the Arsenic down below 10ppb.
The plant has 100psi raw water delivered to it from the well which is about 300ft away.
The water enters the plant and has chlorine and ferric chloride injected about a foot apart in a 2" line about two feet in front of a static mixer.
From the static mixer the water moves 6 feet to a flooded 150gal contact tank where it's jetted in at the top thru a bunch of radial manifold orifices to provide more mixing.
After this delay the water exits the bottom of the contact tank and enters the top of a large flooded filter media tank (about 400gal about 48"dia). There is about 16 inches of free space at the top of this filter above the green sand type media. The media is about 3 feet deep.
The water leaves the bottom of the filter en-route to a 250kgal mountaintop tank. Because of the elevation to the tank all this processing occurs at 100psi.
I've left out the obligatory backwash/holding/reclamation aspects of this description.
The raw As level is about 30ppb. We have done battle here for months and can only get the As -on a good day- down to about 15ppb.
We have tried everything we can think of to get this working.
We added the delay tank thinking we didn't have enough time although most people think the process should take only a few seconds. It didn't help.
It was suggested we needed to reduce the pH. To below 7.0. It's already 6.8.
Things we're seeing that seem odd. While running the plant we've increased the FeCl amounts dramatically and not seen a commiserate stoichiometric change in the Chlorine. Yet we don't see un-oxidized iron leaving the filter.
What could be preventing the take-up of As by the Fe. Even left-field ideas are welcome!
Any discussion would be greatly appreciated.
Keith Cress
kcress -
The plant has 100psi raw water delivered to it from the well which is about 300ft away.
The water enters the plant and has chlorine and ferric chloride injected about a foot apart in a 2" line about two feet in front of a static mixer.
From the static mixer the water moves 6 feet to a flooded 150gal contact tank where it's jetted in at the top thru a bunch of radial manifold orifices to provide more mixing.
After this delay the water exits the bottom of the contact tank and enters the top of a large flooded filter media tank (about 400gal about 48"dia). There is about 16 inches of free space at the top of this filter above the green sand type media. The media is about 3 feet deep.
The water leaves the bottom of the filter en-route to a 250kgal mountaintop tank. Because of the elevation to the tank all this processing occurs at 100psi.
I've left out the obligatory backwash/holding/reclamation aspects of this description.
The raw As level is about 30ppb. We have done battle here for months and can only get the As -on a good day- down to about 15ppb.
We have tried everything we can think of to get this working.
We added the delay tank thinking we didn't have enough time although most people think the process should take only a few seconds. It didn't help.
It was suggested we needed to reduce the pH. To below 7.0. It's already 6.8.
Things we're seeing that seem odd. While running the plant we've increased the FeCl amounts dramatically and not seen a commiserate stoichiometric change in the Chlorine. Yet we don't see un-oxidized iron leaving the filter.
What could be preventing the take-up of As by the Fe. Even left-field ideas are welcome!
Any discussion would be greatly appreciated.
Keith Cress
kcress -